Since the running properties of a tire, especially of a pneumatic vehicle tire, depend to a great extent on the rubber composition of the tread, particularly high demands are placed on the composition of the tread mixture. The partial or complete replacement of the carbon black filler with silica in rubber mixtures has brought the running properties to a higher level overall over the past few years. However, the known trade-offs in the tire properties that behave in a contrary fashion also continue to exist in silica-containing tread mixtures. For instance, an improvement in wet grip and in dry braking still generally entails a deterioration in rolling resistance, in winter properties and in abrasion characteristics.
In order to resolve the trade-offs in the tread, various approaches have already been pursued. For example, a wide variety of different polymers, including modified polymers, resins, plasticizers and finely divided fillers have been used for rubber mixtures, and attempts have been made to influence the vulcanizate properties by modification of the mixture production.
U.S. Pat. No. 6,550,508 discloses, for example, tread mixtures based on carbon black as filler, that comprise, for good grip on ice, inter alia, a liquid polymer, for example, polybutadiene.
U.S. Pat. No. 4,840,988 likewise discloses tread mixtures based on carbon black as filler, that comprise liquid polybutadiene for good winter properties.
Liquid polybutadiene having a high vinyl content and a high glass transition temperature (Tg) is proposed in U.S. Pat. No. 6,242,523 for tire treads as a substitute for conventional plasticizer oils.
However, the use of liquid polybutadiene in conventional mixtures has a very adverse effect on the dry braking and dry handling of tires.
US 2009/0137718 and US 2009/0137701 disclose, as a substitute for customary plasticizer oils, terminally amine-modified liquid polybutadienes or terminally carboxyl-modified liquid polybutadienes in tread mixtures having a high amount of synthetic rubber. The tires are said to feature a very good balance between low fuel consumption and good adhesion properties, and the ability to suppress cracking at the base of profile grooves while simultaneously maintaining wear resistance.
U.S. Pat. No. 8,580,885 discloses a rubber mixture comprising a functionalized polymer having an Mw of 20 000 g/mol and carbon black as filler in combination with 60 phr of natural rubber.
US 2002/0082333 improves processibility by using a triethoxysilane-modified polybutadiene rather than a silane in an NR-free rubber mixture based on synthetic rubber and silica as filler.